Combustion chamber with diverse combustion and diluent air paths



March 11, 1952 R. HUNDSTAD 2,588,723

COMBUSTION CHAMBER WITH DIVERSE COMBUSTION AND DILUENT AIR PATHS Filed June 14, 1948 lNVENTOR RICHARD L Ham smp ATTORNEY Patented Mar. 11,]952

COMBUSTION CHAMBER WITH DIVERSE COMBUSTION AND DILUENT AIR PATHS Richard L. Hundstad, Pittsburgh, Pa., assignor, by mesne assignments, to the United States of America of the Navy as represented by the Secretary Application June 14, 1948, Serial No. 32,928

This invention relates to combustion apparatus, and more particularly to combustion apparatus for a gas turbine power plant.

In order to ensure elficiency and stability of combustion of fuel in a power plant such as a gas turbine engine having a turbine-driven compressor operative to supply air under pressure to a combustion apparatus by way of an annular passageway, it is desirable that the flow of air into the combustion chamber be maintained constant and uniformly distributed. With a combustion burner or shell of the type having walls made of perforated sheet metal, however, the pressure drop which promotes air flow into the upstream end of the combustion chamber falls below that across the downstream end. A relationship is indicated between such a variation in pressure drop within the burner and the velocity of air supplied at ram pressure to the combustion apparatus as a whole. A relatively low pressure drop thus created across the combustion chamber wall in the region of the fuel manifold, may under some conditions induce pressure pulsations and cyclic oscillations of the flame front, resulting in instability of combustion. v It is an object of the present invention to provide an improved combustion apparatus constructed and arranged to maintain substantially stable pressure drop along its length from the upstream end to the downstream end for ob-.

viating the above difiiculty.

Another'object of the invention is the provision of an improved combustion apparatus ineluding a burner shell having a primary air scoop mounted in cooperative relation with the upstream end thereof, and adapted to eifect a relatively increased pressure drop across that region of the shell for avoiding any tendency toward development of unstable or inadequate local air flow conditions.

A further object is the provision of an improved combustion basket structure having means adjacent the upstream end adapted to establish favorable distribution of air supplied to the combustion chamber along the full length thereof, for eliminating variations in pressure drop that otherwise would tend to cause unstable combustion.

These and other objects are effected by the invention as will be apparent from the following description and claims taken in connection with the accompanying drawing, forming=a part of this application, in which:

Fig. 1 is a diagrammatic elevational view, partly in section, of an aviation gas turbine power 3 Claims. (Cl. 6039.65)

plant having combustion apparatus constructed j in accordance with the invention;

Fig. 2 is a fragmentary enlarged detail secstructure ll having mounted along the axis thereof a sectional inner core structure I2, which with the outer casing defines an annular flow passageway l3 that extends longitudinally through the plant from a forwardly-directed air intake opening M to a rearwardly disposed jet nozzle IS. The casing structure II is adapted to be mounted in or on the fuselage or wing of a suitable aircraft (not shown) with the intake ,opening I 4 pointed in the direction of flight.

. structure or burner shell l9 comprises annular Mounted within the power plant in axial alignment are an axial flow compressor ll, combustion apparatus 18 including an annular burner shell or combustion basket [9, and a turbine 20, which is operatively connected to the compressor through the medium of a shaft 2i that is suitably journaled within the casing structure l0.

In accordance with well-known principles of operation. of gas turbine engines, air entering the intake opening I4 is compressed by the compressor ll and delivered. through the passageway 13 to the combustion apparatus l8, where fuel supplied by means of a suitable manifold and nozzles 22 is burned to provide motive fluid for driving the turbine 20. Motive -fluid exhausting from the turbine is then discharged by way of the nozzle IS in the form of a jet establishing a propulsive thrust.

As best shown in Fig. 2, the combustion basket outer and inner walls 25 and 26, each of which includes a number of sections which may be welded or otherwise assembled in overlapping end-to-end relation for providing an annular combustion chamber 2'1, which communicates with the surrounding space or passageway 13 by way of apertures 28 formed in spaced rows along the length of the structure. In the form of basket structure illustrated, annular spacers such as 29 and 30v are interposed between the adjacent ends of the several sections forming the walls 25 and 26, for providing additional flow communications between the passageway 13 and chamber 21. The walls 25 and are preferably tapered at the upstream end of the burner shell 19 and are welded or otherwise suitably joined to the annular fuel manifold 22, through the nozzles of which fuel is injected under pressure into the combustion chamber 2! in the well-known manner. It will thus be apparent that air under pressure supplied through the passageway 13 from the compressor is free to flow into all portions of the combustion chamber 21, the downstream end of which is open at 3i to deliver hot motive fluid to the turbine, as already explained.

According to the invention, an-annular primary air scoop 33 is mounted in encompassing relation with respect to the upstream end of the burner shell IQ for diverting air into the region adjacent the manifold and nozzles 22 at a rate establishing a local pressure drop that will be substantially equalized with the normal pressure drop existing in the downstream end. The scoop 33 may comprise an outer wall 34 and an inner wall 35, which are supported on the burner shell in spaced relation with the tapered walls 25 and 26, respectively, thus defining an annular entryway 36 somewhat in advance of the manifold 22.

With the air scoop 33 thus disposed in cooperative relation with the burner shell l9 adjacent the primary air admission zone thereof, air flowing from the passageway 13 into the entryway 36 will expand into the upstream end of :the combustion chamber 21 from a pressure definitely higher than the normal fluid pressure within the upstream end thereof, so that slight fiuctations in pressure inside the burner will not impede the constant supply of primary :air required for combustion. By properly propoi tioning and positioning the scoop with relation to the burner shell, substantially stable pressure drop throughout the length of the combustion chamber 21 may be attained, establishing a definite ratio between the quantity of air the art that it is not so limited, but is susceptible of various changes and modifications without departing from the spirit thereof.

What is claimed is:

1, In combustion apparatus comprising a casing having an annularpassageway for receiving air under pressure, annular combustion basket structure mounted in said casing and defining a combustion chamber having upstream and downstream inlets communicating with said passage- .way, fuel supply means associated with the upstream end of said basket structure, and a pair of spaced annular imperforate walls interposed in said passageway with the downstream ends thereof connected to opposite sides of said basket structure, said walls extending in spaced overlapping relation with the upstream inlets of said basket structure, said walls being further spaced apart at their downstream end than at their upstream end and defining an annular entryway substantially forward of the fuel supply means to divide air insaid passageway into primary and secondary streams and to guide primary air into the upstream end of said combustion chamber at a rate establishing a definite pressure drop across said upstream end so related to that in the downstream end as to minimize any tendency toward development of backflow or pressure surges during combustion of fuel.

2. In combustion apparatus comprising a casing having an annular passageway for receiving air under pressure, annular combustion basket structure mounted in said casing and defining a combustion chamber having upstream and downstream inlets communicating with said passageway, fuel supply means associated with the upstream end thereof, and a pair of imperforate annular walls spaced apart at opposite sides of said admitted to the upstream portion with'relation to that admitted to the downstream portion for rendering the combustion of fuel therein a steady and :efiicient process. As shown in Fig. 2, the walls '34 and 35 preferably diverge from the forwardly disposed entryway 36, and thus form a diffusing space overlapping the upstream end of the shell structure l9.

In Fig. 3 there is illustrated a single unit 40 of a combustion apparatus of the well-known multiple chamber type, equipped with an air scoop 4i embodying the invention in a different form". The combustion unit 40 may comprise a sectional apertured annular wall structure having inlet openings 42 and a combustion chamber 43 .closed at its upstream end by a fuel nozzle assembly 44, It will be understood that the combustion unit 40 is one of an annular group of similar units mounted within an annular air flow passageway 45 formed with in the casing structure of a power plant. 'In the form illustrated in Fig. 3, the air scoop 4| includes a cylindrical body 5| overlapping the end of the combustion unit 40 adjacent the fuel nozzle assembly, and an inwardly-tapered leading portion 52 forming an entryway 53 for effecting constant flow of primary air into the upstream end of the combustion chamber 43 at a pressure favoring maintenance of the desired stability of the combustion process, as hereinbefore explained.

While the invention has been shown in several forms, it will be obvious to those skilled in upstream end of the basket structure and extending upstream thereof for initially separating incoming air in said passageway into primary and secondary streams, said annular walls diverging rearwardly with the downstream ends of said walls being joined to said basket structure and the forward portions forming an entryway to a diffusing space overlapping the upstream inlets of said basket structure, the primary air stream .beingguided by said walls through said upstream inlets into said combustion chamber at a velocity tending to stabilize the pressure drop throughout said chamber, whereby any tendency toward development .of'undesired variations in air flow is minimized.

3. Combustion apparatus for a gas turbine .power plant having a passage for receiving a stream of air under pressure moving axially therethrough at high velocity, comprising a diverging burner shell mounted in said passage and enclosing a combustion chamber, said burner shell having a-closed upstream apex and a plurality of lateral upstream and downstream apertures formed along 'the axial extent of the shell for admitting air laterally and inwardly to said combustion chamber, fuel supply means mounted in the apex of said burner shell, and an air scoop comprising imperforate wall structure having its downstream end joined to said bru'ner shell in termediate the ends thereof, said wall structure being disposed in diverging relationship with respect to the axis of said power plant and interposed between the apertured upstream portion of said burner shell and the path of air flowing through said passage toward the downstream apertures in the shell downstream of said air 5 scoop to form a diffusing space about the up- REFERENCES CITED stream portion of the burner Shell the upstream The following references are of record in the end of said wall structure extending in advance file of this patent: of the apex of said burner shell to form an entryway directed upstream into said passage, said air 5 UNITED STATES PATENTS scoop acting on the air flowing into said entryway Number Name Date to increase the pressure drop across the up- 2,164,954 Stephens J uiy 4, 1939 stream end of said combustion chamber, facilitat- 2,268,464 Seippel Dec. 30, 1941 ing constant flow of air thereto by Way of the 2,417,445 Pinkel Mar. 13, 1947 upstream apertures for minimizing cyclic oscil- 10 2,447,482 Arnold Aug. 24, 1948 lation of the flame front. 2,448,561 Way Sept. 7, 1943 2,457,157 King Dec. 28, 1948 RICHARD L. HUNDSTAD. 2,510,645 McMahan June 6, 1950 

